This invention relates in general to vacuum sequencing equipment and deals more particularly with a weight sensitive system for controlling the material draw cycle of pellet receivers and the like.
Vacuum sequencing systems are widely used in the plastics industry and in other industries to supply various types of materials to hoppers and to other equipment. A typical application in the plastics industry is in connection with extrusion machines. The vacuum sequencing system includes a plurality of hoppers which serve as receivers for the plastic pellets or powders that are supplied in batches to the extrusion machines. A conduit extends to each hopper from a storage silo, and a vacuum blower applies a vacuum to the hopper in order to draw the pellets through the conduit and into the hopper during the draw cycle of the system. When the hopper has been loaded sufficiently, a dump valve is activated to break the vacuum, thereby terminating the flow of material and effecting discharge of the hopper contents to the extrusion machine.
At present, the material draw cycle of each hopper is normally controlled on a time basis. Each hopper is equipped with a timing device which opens the dump valve after a preset time has elapsed following initiation of the draw cycle. Although control of the material draw cycle by this type of timing system has worked well for the most part, it has not been wholly free of problems. For example, if the hopper has been drawing from a silo which is relatively remote and it is desired to begin drawing from a closer storage box or bin, the timer must be changed to a shorter cycle in order to prevent possible overfill of the hopper. Conversely, if the change is made from a relatively close storage bin to a more distant one, the hopper will not be adequately loaded unless the time is adjusted to operate on a longer cycle. The timing devices also add to the cost involved and result in considerable inconvenience since they must be reset from time to time.
It is the primary object of the present invention to provide, in a vacuum sequencing system, an improved method and control arrangement for accurately controlling the material draw cycle of a receiver based on the weight of material in the receiver. The weight sensitive control arrangement eliminates the need for timing devices and the need to reset the timers each time the conveying distance is changed.
Another object of the invention is to provide a method and control arrangement of the character described wherein the weight of material delivered to the receiver during each draw cycle can be easily and accurately adjusted.
A further object of the invention is to provide a method and control arrangement of the character described which is well adapted to control a ratio valve in a manner to permit accurately controlled quantities of two materials to be loaded into the receiver. This increases the versatility of the system in that it allows the receiver to be used as a ratio proportioner or ratio blender.
An additional object of the invention is to provide a control arrangement of the character described which operates reliably and with repeatable accuracy and which permits the amount of material used by each receiver to be easily determined. In the latter regard, a batch counter is all that is necessary to measure the material use since the weight of each batch is identical.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.